1. Field of the Invention
The present invention relates to elongated magnetic sensors for detecting magnetic patterns printed on, for example, currency bills.
2. Description of the Related Art
A variety of elongated magnetic sensors have been commercialized as magnetic sensors for identifying objects, such as currency bills and securities, having predetermined magnetic patterns printed thereon with, for example, magnetic ink.
The structure of a known elongated sensor is illustrated in FIGS. 7A-7C. FIG. 7A is a plan view showing the magnetosensitive portion of the sensor with a cover detached therefrom. FIG. 7B is a side view showing a long side of the sensor in that state. FIG. 7C is a side view showing a short side of the sensor in that state. In this example, an elongated magnetic sensor 200 includes a case 1′ and magnetoresistive (MR) devices 21A to 21E arranged linearly in the longitudinal direction of the case 1′ with no intervals therebetween. The magnetoresistive devices 21A to 21E include magnetosensitive units 22A to 22E, respectively. The magnetosensitive units 22A to 22E each include two magnetosensitive element arrays extending in the longitudinal direction. The elongated magnetic sensor 200 also includes connection electrodes 23A to 23E electrically connected to the magnetosensitive units 22A to 22E, respectively (three electrodes for each magnetosensitive unit), external connection terminals 24A to 24E disposed on the case 1′ and connected to the connection electrodes 23A to 23E, respectively, and a permanent magnet (not shown) disposed on the back surface of the case 1′ to apply a magnetic field to the magnetosensitive units 22A to 22E. The elongated magnetic sensor 200 senses changes in the magnetic field (changes in magnetic flux density) due to a magnetic pattern provided on an object being conveyed perpendicularly to the longitudinal direction (in the lateral direction) of the magnetosensitive elements to detect the object (see Japanese Patent No. 2921262 (Patent Document 1)).
Magnetosensitive units used for such an elongated magnetic sensor each include separate magnetosensitive elements that are combined to achieve larger changes in the resistance of magnetoresistive devices due to changes in the magnetic field, as disclosed in FIG. 4 of Japanese Unexamined Patent Application Publication No. 2003-107142 (Patent Document 2). A magnetosensitive unit shown in FIG. 4 of Patent Document 2 includes magnetosensitive elements arranged longitudinally at intervals, connection conductors electrically connecting the magnetosensitive elements, and terminal electrodes electrically connected to external connection electrodes.
FIG. 8A is an enlarged plan view of the magnetoresistive device 21C of the elongated magnetic sensor 200 shown in FIGS. 7A-7C having an inner structure shown in FIG. 4 of Patent Document 2. FIG. 8B is a partial plan view showing the arrangement of the magnetoresistive devices 21B to 21D.
In FIGS. 8A and 8B, the magnetosensitive unit 22C of the magnetoresistive device 21C includes magnetosensitive elements 221C arranged longitudinally at intervals D1, magnetosensitive elements 222C arranged in parallel with the magnetosensitive elements 221C, connection conductors 223C connecting the magnetosensitive elements 221C in series, and connection conductors 224C connecting the magnetosensitive elements 222C in series. The magnetosensitive unit 22C also includes a terminal electrode 227C electrically connected to an end of the series connection of the magnetosensitive elements 221C through a connection conductor 2251C, a terminal electrode 226C electrically connected to an end of the series connection of the magnetosensitive elements 222C through a connection conductor 2252C, and a terminal electrode 228C electrically connected to the other ends of the series connections of the magnetosensitive elements 221C and 222C through a connection conductor 2253C. The magnetoresistive device 21C is disposed between the magnetoresistive devices 21B and 21D in the longitudinal direction.
The intervals D1 between the magnetosensitive elements are adjusted so that a detection output produced when a magnetic pattern passes across the intervals D1 is substantially the same as that produced when the magnetic pattern passes across the magnetosensitive elements. However, the intervals D2 between the magnetosensitive elements nearest the contact surfaces of the adjacent magnetoresistive devices (in FIG. 8B, for example, the interval between the magnetosensitive elements of the magnetosensitive unit 22C nearest the magnetosensitive unit 22D and the magnetosensitive elements of the magnetosensitive unit 22D nearest the magnetosensitive unit 22C) are greater than the intervals D1. The magnetosensitive units cannot be extended to the ends of the magnetoresistive devices because a wafer defining a mother board for the magnetoresistive devices is separated into the magnetoresistive devices by dicing or laser cutting. That is, predetermined cutting margins are defined so as not to cut the magnetosensitive units. In addition, the connection conductors are disposed at the ends of the magnetosensitive element arrays in the longitudinal direction. Even if the magnetoresistive devices are disposed with the longitudinal ends thereof in contact with each other, the intervals between the magnetosensitive elements nearest the opposite ends of the adjacent magnetosensitive elements cannot be less than the areas used for the cutting margins and the connection conductors. When a magnetic pattern passes across the intervals D2, therefore, the elongated magnetic sensor 200 may exhibit a significant decrease in detection output and thus fail to detect the magnetic pattern.